(HealthDay News) -- A new study suggests -- but doesn't prove -- that certain players of action video games may lose gray matter in a part of the brain that's linked to mental illness.

On the other hand, the Canadian study suggests, other players may actually benefit from the games.

And a psychologist not involved with the study said there's no evidence that video games are harmful to the brain.

The results indicate that the reported benefits of playing shooting-style video games -- such as improved attention and short-term memory -- "might come at a cost" in terms of lost brain matter in some players, said the study's lead author, Gregory West. He is an assistant professor with the department of psychology at the University of Montreal.

The difference may be the style of playing, the researchers noted.

The new study aimed to better understand the brain effects of so-called first-person and third-person shooting games -- such as Call of Duty, Battlefield, Killzone, or Medal of Honor -- compared to "3-D platform" games in the Super Mario series.

The researchers used a virtual-reality test, MRIs and 90 hours of game-playing involving 100 people who were either expert or nonexpert players. They also used MRIs to assess the impact on the hippocampus, the part of the brain that helps spatial and episodic memory.

The results showed evidence that gray matter in the hippocampus grew in those players who used so-called spatial strategies to find their way in the action video game. But the gray matter shrunk in those who navigated the same games by learned response.

Spatial players create maps in their heads to understand the geography of the world within the game, the researchers explained. And response players use an approach akin to learning a route that you travel every day -- make a right turn here, then a left, then a right -- so that you can drive on mental auto-pilot without thinking.

Those who played the Super Mario games, meanwhile, showed signs of growth in either the hippocampus or another part of the brain called the entorhinal cortex.

The study authors emphasized that they aren't saying that anyone who plays video games will develop a mental illness.

"But we know that those with less gray matter in the hippocampus are more at risk to get conditions like schizophrenia, post-traumatic stress disorder, depression and Alzheimer's disease," said study co-author Veronique Bohbot. She is an associate professor with the department of psychiatry at McGill University in Montreal.

A video game expert called brain studies of game players problematic.

"Given that there are so many areas in the brain, it stands to reason that, by chance alone, some of these areas may randomly differ between any two groups of people," said Chris Ferguson, a professor of psychology with Stetson University in DeLand, Fla.

"Researchers can sometimes make a big deal out of these random differences and ascribe them to something like video games," he said.

Ferguson noted that overall brain research into the effects of the games hasn't revealed problems.

"Despite some wild headlines and press releases from time to time, the research suggests that video game playing is entirely safe for the brain," Ferguson said.

"The aggregate of studies have not suggested that playing video games, even 'violent' ones, cause either short- or long-term brain changes that are problematic or could be called 'brain damage,' " he added.

"Most studies also don't connect the brain differences to actual behavior. So brain studies often function like Rorschach cards, telling you more about what the researchers want to believe than anything actually happening with human behavior," Ferguson suggested.

What should video game players do? Study lead author West suggests that adults play shooter games for only two to three hours a week.

Ferguson noted that research is hinting that video games may reduce stress and improve problem-solving abilities.

"Playing video games should be balanced with other activities: offline socialization, exercise, work and school, family and good sleep," he said. "As long as games are part of a balanced lifestyle, there's no evidence that they cause harmful brain changes."

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